The names "fish oil" and "cod liver oil" are often used interchangeably. Even well-recognized, authoritative journals have referred to cod liver oil as fish oil. This confusion is unfortunate, because the products marketed as fish oil are very different from the ones marketed as cod liver oil. While both oils come from fish, their similarities end there, because nutritionally they are very different.
Sources
Cod liver oil is derived from the livers of cod fish. Fish oil, however, comes from the entire body of the fish. Since the liver processes toxins, oil from cod livers may contain some of these toxins. While this oil is purified during processing, the presence of polychlorinated biphenyls, or PCBs, remains a concern.
Vitamin A Toxicity
Confusing cod liver oil and fish oil can be dangerous, because fish oil is often taken in high doses. For example, people with IgA nephropathy often take 12 g of fish oil per day. This is 11 times more than the usual dose of cod liver oil. A 12 g dose of cod liver oil has 12,000 IU of vitamin A. This dose is dangerous, because 6,000 IU of vitamin A can weaken bones. A 10,000 IU dose can cause birth defects if you are pregnant.
Omega-3 Fatty Acids
People take fish oil because it is high in eicosapentanoic acid and docosahexanoic acid. Both EPA and DHA are omega-3 fatty acids. While most brands of fish oil come in 1 g capsules, the amount of EPA and DHA varies. If the amount of EPA and DHA seems too good to be true, check the serving size, because several brands claim that a serving of fish oil consists of two capsules.
Kidney Disease
Ever since 1999, when James Donadio published results showing that large doses of fish oil retarded the progression of IgA nephropathy, kidney patients ask about the benefits of fish oil. Although more controlled clinical studies need to be conducted to replicate Donadio's findings, many nephrologists are comfortable recommending fish oil, because it produces few adverse affects.
References
- UC Berkeley: Wellness Letter: Cod Liver Oil
- "Current Pharmacological Designs"; Omega-3 and Renal Function in Older Adults; F. Lauretani et al.; 2009
- Foundation for IgA Nephropathy: Fish Oil
- "Journal of the American Society of Nephrology"; The Long-Term Outcome of Patients with IgA Nephropathy Treated with Fish Oil in a Controlled Trial; James V. Donadio, MD; August 1999
- U.S. Department of Agriculture: Cod Liver Oil
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